Force measuring device



June 1952 H. G. BUSIGNIES FORCE MEASURING DEVICE Filed Dec. 7, 1945 2SHEETS-SHEET l IN V EN TOR. HEY/Pl GI MIG/WES HTYDFIVL'Y June 24, 1952H. BUSIGNIES 2,601,259

FORCE MEASURING DEVICE Filed Dec. 7, 1945 2 Sl-lEETS-SHEET 2 A TTURNEYPatented June 24, 1952 UNITED STATES PATENT "OF F ICE FORCE MEASURINGDEVICE Henri G. Busignies, Forest Hills, N. Y., assignor "to FederalTelephone and Radio Corporation, New York, N. Y., a corporation ofDelaware Application December 7, 1945, Serial No. 633,477

2'Clain1s. 1

This invention relates to a method and apparatus for measuring changesin mechanical pressure. More particularly it deals with a device whichchanges its electrical conductance or resistance in response to changesin pressure. One specific application of this device is in a torquemeter.

It is an object of this invention to measure changes in mechanicalpressure in a novel and effective manner.

It is another object to produce a simple electrical device for measuringchanges in pressure which is free from rectifying effects.

Another object is to produce a simple electrical pressure measuringdevice which may be adapted for use as a torque meter.

Another object is to produce a torque meter 7 which may be applied onshort sections of shafts such as in aircraft motors.

Another object is to produce a torque meter which is not materiallyeffected by external forces such as hysterises losses, changes intemperature, rectifier effects, corrosion, etc.

Still other objects and features will appear from time to time in thedescription which fol lows.

Generally speaking, the electrical measuring device of this inventioncomprises: (1) two met- :11 members having contacting surfaces, thesurface of one member having a greater radius of curvature than that ofthe other, and 2) means for measuring the change in potential betweenthe two members when their surfaces are pressed together. The greaterthe pressure between the two surfaces, the greater is the electricalconductivity and the smaller is the electrical resistance between thetwo members, due to the increase in area of contact between the twosurfaces.

These surfaces on the two contacting members may comprise, a sphere anda plane or, for example, a resilient metal ball (such as a ball of aball hearing) held between resilient metal plates. The resilient metalmembers may be made of steel, phosphorous bronze, berylliumcopper, orother highly elastic and resilient metal alloys.

It is desirable that the metal contact between the two surfaces be keptfree from corrosion. This may be done by enclosing the device in asealed chamber, such as in a vacuum, and/or by coating the surfaces witha non-corrosive material which has a high electrical conductivity. It isalso desirable that the metal contacting surfaces do not rectify theelectricity passing through them, particularly if it is an alternatingcurrent, such as steel to steel contact. Sui-table coating substancesfor the contacting members to overcome these difiiculties are gold,silver, platinum, copper, etc. The coating should not be of such "athickness that the resilience of the metal member is materially offected.

The potential applied across the two contacting surfaces may be eitherdirect current or al ternating current. If alternating current isemployed a comparatively low frequency is desirable such as betweenabout 50 and 5,000 cycles per second.

The electrical circuit employed in measuring the change in potentialacross the two surfaces should be comparatively sensitive and may be anysuitable resistance measuring device such as a Wheatstone bridge,potentiometer, or related circuit.

A specific application for the pressure measuring device of thisinvention is in torque meters. The contacting surfaces of the pressuremeasuring device may be mounted either on the shaft in which the torqueis to be measured or may be stationarily mounted away from the shaft andcoupled thereto through a hydraulic brake and piston system, or thelike. If the two surfaces are mounted on the rotating shaft, they may beelectrically connected to slip rings or magneticah ly coupled throughinduction coils surrounding the rotating shaft. If two or more of thecontacting surfaces are employed in a measuring device they may becoupled so that the change in resistance in one accentuates the changein the other such as in a push-pull hook-up. In this type of hook-up itis desirable that the devices be placed under an initial pressure whichis substantially intermediate of the pressure range within which theyare going to be used.

These and other features and objects of the invention will become moreapparent upon consideration of the following detailed description of anembodiment of the invention to be read in connection with theaccompanying drawings in which:

Fig. l is a schematic diagram of one embodiment of this invention whennot under pressure;

Fig. 2 is a schematic diagram of the embodiment shown in Fig. 1 whenunder pressure;

Fig. 3 is a partial section of the same embodiment employed in a torquemeter;

Fig. 4 is a sectional view along the lines as of Fig. 3; and

Figs. 5, 6, '7 and 8 are schematic wiring dia- 3 grams of alternatingcurrent circuits which may be employed in connection with the torquemeter shown in Figs. 3 and 4.

Referring specifically to Figs. 1 and 2, there is schematically shown aresilient steel ball I, which may be silver or gold plated, held betweentwo steel plates 2, the adjacent surfaces of which may also be similarlyplated. These plates 2 are connected through wires 3 in series with apotential source 4 and meter 5. This meter may be of any suitable designwhich is responsive to the change in flow of current from the batterythrough the wires 3, plates 2, and ball I. The area of contact betweenthe plates 2 and the ball I in Fig. 1 is shown at 6 to be comparativelysmall so that the resistance of the circuit is correspondinglycomparatively large. In order to change the flow of current in thecircuit pressure is applied in the direction of the arrow l to flattenthe ball I as shown in Fig. 2 forming an area of contact 8 substantiallylarger than 6, thereby decreasing the resistance of the ball and platesl and 2 causing more current to flow through the circuit and meter 5.Thus, the needle 9 of the meter indicates a higher reading than isindicated in Fig. 1. The scale of the meter 5 may be calibrated to readdirectly in pounds, of other units corresponding to the pressure appliedin the direction of the arrows l.

The pressure responsive device corresponding the ball I and plates 2 maybe utilized in many different types of apparatus. One specific type isthat of a torque meter specifically disclosed in Figs. 3 and 4.Referring now to Figs. 3 and 4, the ball I and plates 2 are shownclamped between a pair of jaws l0 and II, respectively, integrallyconnected with sleeves l2 and I3 fixedly connected to the shaft [4 bypins or other suitable means and 16, at the two spaced points on theshaft 14. The distance between these points may be as small as four orfive inches and the shaft may be of substantially the same diameter asthe distance between these points. It is desirable, since the member Iand 2 are electrically coupled, to provide suitable insulation betweenthe jaws IO and H and the shaft [4 at H, and also between the plates 2and jaws l0 and ll at 18. Suitable insulating and guiding blocks l9 andmay be provided around the ball I to hold it in place.

Also, integrally mounted on the sleeves l2 and i3 may be an additionalpair of jaws 2| and 22, similar respectively to jaws IO and H. Betweenthese jaws l0 and H may be mounted a ball and plate device 23 and 24,similar to l and 2, and shown in dotted lines in Fig. 3. It is desirablethat the pair of jaws 2i and 22 be axially spaced from the pair ID and II so that suitable electrical connections may be made to them as will bedescribed later.

Although the plates 2 and 24 may be electrically connected with ameasuring instrument by means of slip rings surrounding the jaws andshaft, it is desirable that a non-contacting coupling be made betweenthe measuring instrument and these plates. One form of such a couplingis a magnetic coupling similar to that shown in Figs. 3 and 4 wherein analternating current is employed in the coupling circuit. In theembodiment shown, the plates 2 and 24 are respectively connected tosubstantially low resistance electrical conductors 25, such as a seriesof split copper rings, which surround the shaft and jaw members and areintimately connected (such as by welding or soldering) to the two plates2 and 24. These rings 25 form a secondary of a transformer circuit, theinductance in which may be increased by suitable laminated iron ringchannels 26 surrounding the shaft between the secondary rings 25 and thejaw members 10 and I l This secondary coil assembly, comprising therings 25 and core 26, is mounted to turn with the shaft 14 and may befixedly mounted to one of the jaws, preferably jaw l I, through aninsulating layer 21.

Magnetically coupled to the secondary rings 25 is a stationary primarycoil 28 which may be surrounded by laminated irong ring channels 29. Thecomparatively many turns of the wire in stationary coil 28 is thencoupled to an electrical measuring circuit which will be describedlater.

Similarly the plates 24 are electrically coupled to a rotating secondarycoil assembly 30 which may be fixedly connected to the jaw member 22 forrotation therewith. Surrounding the rotating secondary assembly 30 is astationary primary coil assembly 32, similar to 28 and 29.

The only connections between the primary and secondary coils are airgaps 33 and 34 between the two coil assemblies.

It is desirable that the pressure device l--2 and the pressure device23-24 operate in opposition to each other, i. e., when one is beingcompressed the other is being released. This produces a greater effectin the outside electrical measuring circuit. In such a hook-up it isdesirable that both pressure devices |2, and 2324 be placed under aninitial pressure by means of the screws 35 in each of the jaw members10, ll, 2| and 22. This initial pressure should approximate theintermediate pressure of the range over which these devices are torespond.

Referring to Figs. 5, 6, 7 and 8, there are shown four differentschematic wiring diagrams for coupling the primary and secondary coilsof the two pressure devices employed in the torque meter shown in Figs.3 and 4. In these wiring diagrams the pressure devices l2 and 23-44 areschematically shown and similarly numbered as are the primary andsecondar coils 25 and 28.

Referring specifically to the diagram in Fig. 5, the coils 28 form twolegs of a Wheatstone bridge across a stabilized alternating currentsource 36. The two stationary field coils 39 in the meter form the othertwo legs of the bridge. Coupling the junctures of the legs is a movablecoil 40 to which is connected the needle 4| which cooperates with ascale (not shown) for indicating the amount of unbalance of the bridge.It can be seen that changes in the resistance of the secondary circuits25 will correspondingly change the impedance of the primary circuits 28,thus unbalancing the bridge and causing the coil 40 to turn with theneedle 4|.

Referring to the circuit in Fig. 6 there is shown an alternating currentsupply source 42 in the meter a stationary field coil 43 and movablecoils 44 connected to needle 45. In this circuit it is not necessarythat the alternating supply current be stabilized. This particularcircuit is adapted for use where the variation of the coil is large withrespect to the fixed value in coil 43.

Referring to Fig. 7, there is shown still another possible circuithaving an alternating current source 46 (which may or may not bestabilized), and in the meter stationary field coils 4'! and 43 andmovable field coils 49 connected to needle 45. In this circuit doublecrossed coils 48 and 43 are coupled so that the differences in currentin the coils 48 and 49 on the left is compared with the sum of thecurrent in the coils 48 and 49 on the right.

Referring to Fig. 8, there is shown an alternating current supply 5!which need not be stabilized, stationary field coils 52, 53, 54, 55 and56, and movable coils 51 coupled to the needle 58. The double crossedcoils 51 form a transformer to produce a sum current effect reducing thevalue of the field due to the fixed coils 5256 thereby increasing thedeflection of the needle 58 with respect to that obtained for a similaramount of current in the circuit shown in Fig. 6.

The crossed coils shown in the circuits above described may make anangle with each other larger than 90", if such is desirable.

Although only one application of the pressure responsive device of thisapplication has been disclosed, it is obvious from the foregoingdescription that it has other applications not only for measuring thedifference in forces in other types of torque meters, but differences inforces generally including electric weighing equipment.

While the above is a description of the p nciples of this invention inconnection with specific apparatus and a particular modificationthereof, it is to be clearly understood that this description is madeonly by way of example and not as a limitation on the scope of thisinvention as defined in the accompanying claims.

I claim:

1. A torque meter comprising: a shaft in which the torque is to bemeasured, a pair of jaws rigidly attached to said shaft at differentaxially spaced points and extending into spaced overlapping relationshipwith one another, a resilient metal ball clamped between two resilientmetal plates between said jaws, said ball and at least one of said metalplates being electrically insulated from said shaft, means for applyinga potential between one of said plates and the other through said ball,and means for measuring the resistance between said plates according tothe change in pressure on said plates by said jaws in proportion to thetorque in said shaft between said spaced points, whereby variations inthe pressure between said plates produce variations in the contact areasbetween said ball and said plates which produce variations in theresistance between said plates.

2. A device for measuring shaft torque comprising a pair of jaws rigidlyattached to said shaft at different axially spaced points and extendinginto spaced overlapping relationship with one another, a resilient metalball, a pair of resilient metal plates said plates being respectivelyattached to each of said jaws said ball being clamped between saidplates, said ball and said plates being electrically insulated from saidshaft, 9. source of electric potential, means to apply said potentialbetween said plates and said ball, means for measuring the change ofelectrical resistance between said plates and said ball whereby thevariations in pressure between the spaced points on said shaft to whichsaid jaws are attached produce variations in the contact areas betweensaid ball and said plates thus producing corresponding changes ofelectrical resistance between said plates.

HENRI G. BUSIGNIES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,681,314 Vawter Aug. 21, 19281,695,295 Rollins Dec. 18, 1928 1,781,002 Pelterie r Nov. 11, 19302,049,330 Smith July 28, 1936 2,415,513 Martin et al Feb. 11, 19472,419,217 Isenberg Apr. 22, 1947 2,426,396 Isenberg Aug. 26, 1947FOREIGN PATENTS Number Country Date 470,454 Germany r- Jan. 15, 1929226,861 Great Britain Dec. 19, 1924 529,843 Germany July 17, 1931 OTHERREFERENCES Publication, Journal of the Institute of Electrical Engineers(British), July 1045, page 287.

